Photo-oxidants for energy conversion and catalysts and systems and methods of using same

ABSTRACT

High-potential photo-oxidants are provided with a supermolecule structure at least including a conjugated macrocycle linked to a metal complex. The conjugated macrocycle is electron-accepting relative to hydrogen or bears electron withdrawing substituents such as fluoroalkyl, fluoroaryl, fluoro, halo, cyano, or nitro. The metal complex is also electron-accepting relative to hydrogen or bears electron withdrawing substituents such as fluoroalkyl, fluoroaryl, fluoro, halo, cyano, or nitro. The linker can be thynyl, vinyl, thiophenyl, diethynylaryl, divinylaryl, diethynyl (unsaturated heterocycloalkenyl), divinyl (unsaturated heterocycloalkenyl), diethynyl (unsaturated heterocycloalkynyl), or divynyl (unsaturated heterocycloalkynyl). A specific implementation is an ethyne-bridged eDef-Rutpy-(porphinato)Zn(II) (eDef-RuPZn) supermolecule.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/514,994, filed Jun. 5, 2017.

GOVERNMENT SUPPORT

This invention was made with government support under Grant No.CHE-1413333 awarded by the National Science Foundation. The U.S.Government has certain rights in this invention.

BACKGROUND

Photochemistry and catalysis are two of the many areas of interest forenergy generation and efficiencies in chemical reactions. Photochemistryinvolves chemical reactions caused by absorption of light in the visiblerange (as well as ultraviolet and infrared light). Catalysis involvesaccelerating (or in some cases slowing) the rate of chemical reaction.Applications currently being considered include light-driven wateroxidation in dye-sensitized photoelectrosynthesis cells (DSPECs),photoredox catalysis of organic transformations, and photodecompositionof heavily halogenated hydrocarbon wastes.

DSPECs are used to produce solar fuels by splitting water into H₂ and O₂or by solar-driven reduction of CO₂ by water to carbon-based fuels.Current DSPECs integrate molecular level light absorption and catalysiswith the bandgap properties of stable oxide materials such as TiO₂ andNiO. Excitation of surface-bound chromophores of the current DSPECsleads to excited state formation and rapid electron or hole injectioninto the conduction or valence bands of n or p-type oxides.

Photoredox catalysis of organic transformations uses the energy of lightto accelerate the chemical reaction of organic compounds viasingle-electron transfer. Photoredox catalysis can be used to enablechallenging bond constructions not typically available under standardprocesses by exploiting the energy gained by the absorption of light(which is relatively low energy) by the catalyst.

Halogenated hydrocarbon wastes are a type of hazardous waste materials,which can benefit from being decomposed. Photodecomposition can providean efficient and relatively safe manner of doing so.

These and other applications can benefit from high potentialphoto-oxidants that feature comprehensive absorptivity in the visiblespectral domain and long-lived excited states.

BRIEF SUMMARY

Photo-oxidants for energy conversion and catalysts and systems andmethods of using same are described. The described photo-oxidantsinclude high-potential chromophores capable of power a range oflight-driven oxidation reactions. Chromophores are provided that notonly exhibit a high electrode potential (e.g., excited-state reductionpotential), but also support a higher range (of wavelengths) ofabsorptivity. These chromophores and systems, as well as relatedcompositions, can also be used to drive challenging photo-oxidationreactions for applications such as energy conversion and photocatalysis.

A composition is provided given by the structure:

In the above given structure, L=ethynyl, vinyl, thiophenyl,diethynylaryl, divinylaryl, diethynyl(unsaturated heterocycloalkenyl),divinyl(unsaturated heterocycloalkenyl), diethynyl(unsaturatedheterocycloalkynyl), or divynyl(unsaturated heterocycloalkynyl). M₁ isconjugated with a macrocycle bearing an electron withdrawing substituent(or a macrocycle that is electron accepting relative to hydrogen); andM₁=Zn, Mg, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Cd, Ge, Sn, Hf,Ta, W, Re, Os, Ir, Pt, Au, or Pb. M₂ is complexed with electronwithdrawing ligands (or is electron accepting relative to hydrogen); andM₂=Fe, Ru, Os, Re, Ir, Rh, or Pt. In addition, R₁, R₂═F, C_(x)F_(2x+1),CN, NO₂,

In some cases, a compound is provided with a formula of A-ethyne-B,where A is a conjugated macrocycle bearing fluoroalkyl, fluoroaryl,fluoro, or other electron withdrawing substituents such as halo, cyano,or nitro, or is electron-accepting relative to hydrogen; and B is ametal complex that also bears fluoroalkyl, fluoroaryl, fluoro, or otherelectron withdrawing substituents such as halo, cyano, or nitro, or iselectron-accepting relative to hydrogen.

In some cases, a compound is provided with a formula of A-L-B, wherelinker L is ethynyl, vinyl, thiophenyl, diethynylaryl, divinylaryl,diethynyl(unsaturated heterocycloalkenyl), divinyl(unsaturatedheterocycloalkenyl), diethynyl(unsaturated heterocycloalkynyl), ordivynyl(unsaturated heterocycloalkynyl); A is a conjugated macrocyclebearing fluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen; and B is a metal complex that also bearsfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen.

In some cases, a compound is provided with a formula ofA-ethyne-B-ethyne-A, where A is a conjugated macrocycle bearingfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen; and B is a metal complex that also bearsfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen.

In some cases, a compound is provided with a formula ofB-ethyne-A-ethyne-B, where A is a conjugated macrocycle bearingfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen; and B is a metal complex that also bearsfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen.

In some cases, a compound is provided with a formula of A-L-B-L-A, wherelinker L is ethynyl, vinyl, thiophenyl, diethynylaryl, divinylaryl,diethynyl(unsaturated heterocycloalkenyl), divinyl(unsaturatedheterocycloalkenyl), diethynyl(unsaturated heterocycloalkynyl), ordivynyl(unsaturated heterocycloalkynyl); A is a conjugated macrocyclebearing fluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen; and B is a metal complex that also bearsfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen.

In some cases, a compound is provided with a formula of B-LA-L-B, wherelinker L is ethynyl, vinyl, thiophenyl, diethynylaryl, divinylaryl,diethynyl(unsaturated heterocycloalkenyl), divinyl(unsaturatedheterocycloalkenyl), diethynyl(unsaturated heterocycloalkynyl), ordivynyl(unsaturated heterocycloalkynyl); A is a conjugated macrocyclebearing fluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen; and B is a metal complex that also bearsfluoroalkyl, fluoroaryl, fluoro, or other electron withdrawingsubstituents such as halo, cyano, or nitro, or is electron-acceptingrelative to hydrogen.

In an example implementation, an electron-deficient (eDef)high-potential chromophore capable of powering a broad range oflight-driven oxidation reactions is provided as an ethyne-bridgedeDef-Rutpy-(porphinato)Zn(II) (eDef-RuPZn) supermolecule. eDef-RuPZn isshown to be endowed with intense panchromatic absorptivity, a largemagnitude excited-state reduction potential, and long-lived, highlyoxidizing singlet and triplet charge-transfer (CT) excited states.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. While several implementations and examplesare described in connection with these drawings, the disclosure is notlimited to the implementations and examples disclosed herein.

FIG. 1A shows an example general structure of a chromophore as describedherein for energy conversion and photocatalysis applications.

FIG. 1B shows example structural formulas for a macrocycle in theexample general structure of FIG. 1A.

FIG. 1C shows example structural formulas for a surrounding array ofbound complexing agents, or ligands, in the example general structure ofFIG. 1A.

FIG. 2A shows electronic absorption spectra of eDef-Rutpy and eDef-RuPZnin acetonitrile solvent.

FIG. 2B shows a plot of total integrated absorptive oscillator strengthsfor eDef-Rutpy and eDef-RuPZn.

FIG. 3A shows a representative ultra-fast transient absorption spectrarecorded at several time delays for eDef-Rutpy.

FIG. 3B shows representative ultra-fast transient absorption spectrarecorded at several time delays for eDef-RuPZn.

FIG. 4 illustrates redox potentials from potentiometric data of Ru(tpy)₂²⁺, eDef-Rutpy, RuPZn and eDef-RuPZn.

FIG. 5 illustrates a synthetic route to eDef-Rutpy and eDef-RuPZnaccording to an example method.

FIG. 6 shows Proton NMR spectrum of eDef-Rutpy in CD₃CN.

FIG. 7 shows Proton NMR spectrum of eDef-RuPZn in CD₃CN.

FIG. 8 shows Electronic absorption spectrum of RuPZn in acetonitrilesolvent.

FIG. 9 shows Electronic absorption spectra of eDef-RuPZn (in MeCN),eDef-Rutpy (in MeCN) and[5-ethynyl-10,15,20-tris(heptafluoropropyl)porphinato]zinc(II) (in THF)building blocks; and room-temperature emission spectra (fluorescence at700 nm and phosphorescence at 810 nm, excitation wavelength=628 nm) ofeDef-RuPZn in acetonitrile solvent.

FIG. 10A shows a 77K Emission spectrum (excitation wavelength=510 nm) ofeDef-Rutpy in butyronitrile, and the absorption spectrum of eDef-Rutpyat RT (room temperature) in acetonitrile.

FIG. 10B shows a Gaussian fitting of the 77K emission data of FIG. 10A,with labeled energy (2.09 eV) at which the emission intensity is 10%that of the highest emission intensity

FIG. 11 shows a 77K emission spectrum (fluorescence at 600750 nm andphosphorescence at 750850 nm, excitation wavelength=590 nm) ofeDef-RuPZn in butyronitrile, and the absorption spectrum of eDef-RuPZnin acetonitrile.

FIG. 12A shows plots of a room-temperature (RT) emission spectrum(excitation wavelength=628 nm) of eDef-RuPZn in deaerated acetonitrilesolvent, 77K emission spectrum (excitation wavelength=628 nm) ofeDef-RuPZn in butyronitrile, along with the absorption spectrum ofeDef-RuPZn in acetonitrile.

FIG. 12B shows Gaussian fitting of the RT emission data of FIG. 12A,with labeled energy (1.65 eV) at which the emission intensity is 10%that of the highest emission intensity.

FIG. 12C shows Gaussian fitting of the 77K emission data of FIG. 12A onenergy scale, with labeled energy (1.61 eV) at which the emissionintensity is 10% that of the highest emission intensity.

FIG. 13 shows potentiometric data of eDef-Rutpy (vs. SCE) in 0.1 MTBAPF₆/acetonitrile electrolyte/solvent system.

FIG. 14 shows potentiometric data of eDef-RuPZn (vs. SCE) in 0.1 MTBAPF₆/acetonitrile electrolyte/solvent system.

FIG. 15 shows representative time traces (black) from femtosecondpump-probe transient absorption of eDef-Rutpy in acetonitrile solventfor 461 nm, 499 nm, 520 nm, and 738 nm wavelengths.

FIG. 16 shows representative time traces (black circles) fromfemtosecond pump-probe transient absorption of eDef-RuPZn inacetonitrile solvent for 509 nm, 533 nm, 607 nm, 668 nm, 732 nm, 824 nm,901 nm, and 1010 nm wavelengths.

FIG. 17 shows plots of decay-associated difference spectra (DADS) ofeDef-RuPZn derived from a global fit of pump-probe transient absorptiondata from FIG. 13 in acetonitrile solvent; the lifetimes associated witheach spectrum are labeled in the inset. τ₁=290 fs corresponds to thesolvent relaxation timescale; τ₂=13.5 ps is the timescale of S₁→T₁intersystem crossing (ISC), characterized by a rise (negative fitamplitude) in transient absorption in the NIR; The small-amplitude,longer-timescale time constant, τ₃=340 ps, is assigned to structuralrelaxation of the long-lived T₁ state of eDef-RuPZn.

FIG. 18 shows a plot of nanosecond pump-probe transient absorptionspectra of eDef-RuPZn in acetonitrile solvent following excitation at520 nm; inset shows kinetics at a representative wavelength overlaidwith single-exponential fit (τ=92.5 μs).

FIG. 19 shows a time-resolved emission of RuPZn in acetonitrile solventwith its fit to a mono-exponential function convoluted with theexperimentally determined instrument response function (IRF).

DETAILED DESCRIPTION

Photo-oxidants for energy conversion and catalysts and systems andmethods of using same are described. The described photo-oxidantsinclude high-potential chromophores capable of power a range oflight-driven oxidation reactions. Chromophores are provided that notonly exhibit a high electrode potential (e.g., excited-state reductionpotential), but also support a higher range (of wavelengths) ofabsorptivity. These chromophores and systems, as well as relatedcompositions, can also be used to drive challenging photo-oxidationreactions for applications such as energy conversion and photocatalysis.

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to certain embodiments ofthe invention and specific language will be used to describe the same.It will nevertheless be understood that no limitation of the scope ofthe disclosure is thereby intended, such alteration and furthermodifications of the disclosure as illustrated herein, beingcontemplated as would normally occur to one skilled in the art to whichthe disclosure relates.

Articles “a” and “an” are used herein to refer to one or to more thanone (i.e. at least one) of the grammatical object of the article. By wayof example, “an element” means at least one element and can include morethan one element.

Unless otherwise defined, all technical terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this disclosure belongs.

Chromophores refer to molecules that can absorb certain wavelengths oflight.

As described in more detail herein, high-potential chromophores capableof power a range of light-driven oxidation reactions are provided withcompounds including a conjugated macrocycle and a metal complex.

Conjugation is the overlap of p-orbitals across a 6 bond (sigma bond).In transition metals, d-orbitals may overlap. The orbitals havedelocalized electrons when there are alternating single and multiplebonds in a molecule. Bonds alternate in a chain so long as each atom hasan available p-orbital. Conjugation tends to lower the energy of themolecule and increase its stability. Conjugated systems can formchromophores.

Macrocycles have interior and exterior sites, which may be subject tosite-specific substitution; and are often described as a moleculecontaining twelve or more atoms with at least one large ring.

A metal complex is also referred to as a coordination compound. Metalcomplexes or metal clusters can interact with or are stabilized bycontact with the surface of inorganic carriers of oxides such as silicagel, alumina, and titanium dioxide, and by encapsulation in molecularsieves like zeolites, aluminum phosphates, or layer silicates likehectorite clays. A metal complex consists of a central metal atom or ionthat is bonded to one or more ligands, which are ions or molecules thatcontain one or more pairs of electrons that can be shared with themetal. Metal complexes can be neutral; positively charged; or negativelycharged. Electrically charged metal complexes are sometimes calledcomplex ions. A coordination compound contains one or more metalcomplexes.

A composition is provided given by the structure:

FIG. 1A, and the above structure, shows an example general structure ofa chromophore as described herein for energy conversion andphotocatalysis applications.

In the example general structure, L=ethynyl, vinyl, thiophenyl,diethynylaryl, divinylaryl, diethynyl(unsaturated heterocycloalkenyl),divinyl(unsaturated heterocycloalkenyl), diethynyl(unsaturatedheterocycloalkynyl), or divynyl(unsaturated heterocycloalkynyl). M₁ isconjugated with a macrocycle bearing an electron withdrawing substituent(or a macrocycle that is electron accepting relative to hydrogen); andM₁=Zn, Mg, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Cd, Ge, Sn, Hf,Ta, W, Re, Os, Ir, Pt, Au, or Pb. M₂ is complexed with electronwithdrawing ligands (or is electron accepting relative to hydrogen); andM₂=Fe, Ru, Os, Re, Ir, Rh, or Pt. In addition, R₁, R₂═F, C_(x)F_(2x+1),CN, NO₂,

FIG. 1B shows example structural formulas for a macrocycle 110 in theexample general structure of FIG. 1A; and FIG. 1C shows examplestructural formulas for a surrounding array 120 of bound complexingagents, or ligands, for M₂ in the example general structure of FIG. 1A.

In some cases, the composition can be given by the structure:

where M₁=Zn, Mg, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Cd, Ge, Sn,Hf, Ta, W, Re, Os, Ir, Pt, Au, or Pb; M₂=Fe, Ru, Os, Re, Ir, Rh, or Pt;and R₁₋₈═F, C_(x)F_(2x+1), CN, NO₂,

where x, y, z and i are integers.

In some cases, the composition can be given by the structure:

where M₁=Zn, Mg, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Cd, Ge, Sn,Hf, Ta, W, Re, Os, Ir, Pt, Au, or Pb; M₂=Fe, Ru, Os, Re, Ir, Rh, or Pt;and F, C_(x)F_(2x+1), CN, NO₂,

where x, y, z and i are integers.

It should be noted that the above structures are just two examplestructures according to the general structure composition of FIGS.1A-1C.

In various implementations, a compound having a formula of (1)A-ethyne-B, (2) A-ethyne-B-ethyne-A, (3) B-ethyne-A-ethyne-B, (4) A-L-B,(5) A-L-B-L-A, or (6) B-L-A-L-B can be used, where A is a conjugatedmacrocycle bearing an electron withdrawing substituent or iselectron-accepting relative to hydrogen; and B is a metal complexbearing an electron withdrawing substituent or is electron-acceptingrelative to hydrogen.

An electron withdrawing group refers to an atom or group that drawselectron density from neighboring atoms, such as from a reaction center,towards itself, usually by resonance or inductive effects. Resonancerefers to a system in oscillation due to some external force. Inductiveeffects refer to the effect on electron density in one portion of amolecule due to electron-withdrawing or electron-donating groupselsewhere in the molecule. Further, electron withdrawing groups can beidentified through routine experimentation by, for example, substitutionin a molecule and testing of any resultant inductive effects.

The electron withdrawing substituent for A can be selected from thegroup or a subset of the group consisting of fluoroalkyl, fluoroaryl,fluoro, halo, cyano, and nitro. Similarly, the electron withdrawingsubstituent for B can be selected from the group or a subset of thegroup consisting of fluoroalkyl, fluoroaryl, fluoro, halo, cyano, andnitro. In some cases, the electron withdrawing substituent for A, B, orboth is perfluoroalkyl or perfluoroaryl.

In some cases, the macrocycle is a porphyrin, porphycene, rubyrin,rosarin, hexaphyrin, sapphyrin, chlorophyl, chlorin, phthalocyanine,porphyrazine, bacteriochlorophyl, pheophytin, texaphyrin, or relatedmacrocyclic-based component, that is capable of binding a metal ion.

A porphyrin refers to a derivative of porphine, a conjugated cyclicstructure of four pyrrole rings (a five-membered ring containing anitrogen atom) linked through their 2- and 5-positions by methinebridges. A porphyrin has four of its nitrogen atoms facing the center,which can capture a metal ion to form a very stable organometalliccomplex Porphyrins can bear up to 12 substituents at meso (i.e., o) andpyrrolic (i.e., B) positions thereof. (See, e.g. U.S. Pat. No.5,371,199, which is incorporated by reference).

In some cases, the conjugated macrocycle is a porphyrin complexed tometal atom M₁. The metal atom M₁ can be selected from the group or asubset of the group consisting of Zn, Mg, Cr, Fe, Co, Ni, Cu, Zr, Nb,Mo, Ru, Rh, Pd, Cd, Ge, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au, or Pb. Forexample, M₁ can be selected from the group consisting of Zn, Co, Ni, Fe,Pt, and Pd.

In some cases, the metal complex is a (polypyridyl)metal species. Insome cases, the polypyridyl ligand of the (polypyridyl)metal species isterpyridyl or bipyridyl. In some cases, the metal complex is a(poly-heterocyclic)metal species. In some cases, the metal complexincludes a transition metal (a metal in Groups 1B-8B). In some cases,the metal complex includes a Group 8 transition metal (Fe, Ru, Os, orHs). In some cases, the metal complex includes a transition metalselected from the group consisting of Fe, Ru, Os, Rh, Ir, and Pt. Themetal complex may be neutral or charged (e.g., positively charged ornegatively charged).

For formulas with linker L (e.g., 4, 5, and 6), linker L can be ethynyl,vinyl, thiophenyl, diethynylaryl, divinylaryl, diethynyl(unsaturatedheterocycloalkenyl), divinyl(unsaturated heterocycloalkenyl),diethynyl(unsaturated heterocycloalkynyl), or divynyl(unsaturatedheterocycloalkynyl).

The described compounds may be characterized according to their singletexcited-state reduction potential, triplet excited-state reductionpotential, singlet excited-state lifetime, triplet excited-statelifetime, and/or total integrated absorptive oscillator strengths. Insome cases, a compound according to any of the described formulas has asinglet excited-state reduction potential (¹E^(−/)*) of at least 1.50 V.In some cases, a compound according to any of the described formulas hasa triplet excited-state reduction potential (³E^(−/)*) of at least 1.20V. In some cases, a compound according to any of the described formulashas a singlet excited-state lifetime of at least 10 ps. In some cases, acompound according to any of the described formulas has a tripletexcited-state lifetime of at least 1 μs. In some cases, a compoundaccording to any of the described formulas has a total integratedabsorptive oscillator strengths calculated over the 26,300 cm⁻¹ (380 nm)to 14,280 cm⁻¹ (700 nm) spectral range at least five times larger thanthat determined for the benchmark compound Ru(tpy)²⁺.

In an example implementation of the described compounds, anelectron-deficient (eDef) high-potential chromophore capable of poweringa broad range of light-driven oxidation reactions is provided as anethyne-bridged eDef-Rutpy-(porphinato)Zn(II) (eDef-RuPZn) supermolecule(A=eDef-Rutpy-(porphinato)Zn(II); B=eDef-RuPZn; L=ethyne). eDef-RuPZn isshown to be endowed with intense panchromatic absorptivity, a largemagnitude excited-state reduction potential, and long-lived, highlyoxidizing singlet and triplet charge-transfer (CT) excited states.

(Polypyridyl)metal complexes like Ru(tpy)22+ and Ru(bpy)32+ have been afocus of attention for light-driven oxidation reactions for energyconversion and photocatalysis applications. However, correspondingelectron-deficient (eDef) high-potential chromophores capable ofpowering a broader range of light-driven oxidation reactions have shownlittle progress. Typically, eDef chromophores suffer from a combinationof short excited state lifetimes, limited vis-spectral domainabsorptivity, or photochemical instability.

Given challenges commonly associated with cross-coupling reactionsinvolving 2-pyridyl derivatives, syntheses of eDef-Tpy and eDef-TpyBrprecursor ligands defined key obstacles to the target eDef-Rutpy andeDef-RuPZn chromophores. eDef-RuPZn was constructed via Sonogashiracross-coupling of [5-ethynyl-10, 15,20-tris(perfluoropropyl)porphinato]Zn(II) and eDef-RutpyBr fragments.The syntheses of eDef-Rutpy and eDef-RuPZn chromophores are described indetail with respect FIG. 5.

FIG. 2A shows electronic absorption spectra of eDef-Rutpy and eDef-RuPZnin acetonitrile solvent; and FIG. 2B shows a plot of total integratedabsorptive oscillator strengths for eDef-Rutpy and eDef-RuPZn. In FIG.2B, the plot of total integrated absorptive oscillator strengths werecalculated over the 26316 cm¹ (380 nm) to 14286 cm¹ (700 nm) spectralrange (see Turro, N. J. Principles of Modern Molecular Photochemistry;University Science Books: Sausalito, Calif., 2009).

The electronic absorption spectrum (EAS) of eDef-Rutpy in acetonitrilesolvent bears a close resemblance to that of Ru(tpy)₂ ²⁺ (FIG. 2B).eDef-Rutpy evinces ligand-localized π-π* transitions over the 260-350 nmrange (λ_(max)=275 nm, ε=53100 M⁻¹ cm⁻¹; λ_(max)=315 nm, ε=66500 M⁻¹cm⁻¹), and a weaker MLCT manifold spanning the 400-600 nm spectralwindow (λ_(max)=482 nm; ε=17600 M⁻¹ cm⁻¹), akin to those characteristicof Ru(tpy)₂ ^(2|) [π-π* (λ_(max)=271 nm, ε=46800 M⁻¹ cm⁻¹; λ_(max)=307nm, ε=68700 M⁻¹ cm⁻¹); MLCT (λ_(max)=476 nm, ε=17700 M⁻¹ cm⁻¹)]. Thesimilarities between the steady-state EAS of eDef-Rutpy and Ru(tpy)₂ ²⁺suggest that the six CF₃ groups of the former implement theelectron-withdrawing effect through the ligand a-bond network, withoutsubstantially perturbing the character of the n-electron system. Ineffect, the nature of the electronic transitions of eDef-Rutpy isunperturbed relative to Ru(tpy)₂, while eDef-Rutpy becomes uniformlymore oxidizing (see below). However, the lack of significant oscillatorstrength in the visible remains a limitation of both Ru(tpy)₂ andeDef-Rutpy for light-driven reactions.

As can be seen in FIG. 2B, directly addressing the issue of visibleabsorptivity, the EAS of eDef-RuPZn features almost eight times theoscillator strength as that of eDef-Rutpy in the 380-700 nm visiblespectrum range, and displays spectral features similar to those evincedby RuPZn. The porphyrin B-state derived transition centered at 441 nmmanifests an absorption maximum that exceeds 1.2×10⁵ M⁻¹ cm⁻¹. Thetransition centered at 504 nm (ε=75400 M⁻¹ cm⁻¹) derives from the Ru(II)complex MLCT band and oscillator-strength mixing involving the porphyrinmoiety. Note that the weakest eDef-RuPZn absorption bands at 582 nm(ε=26100 M⁻¹ cm⁻¹) and 614 nm (ε=18600 M⁻¹ cm⁻¹) are more intense thanthe Ru(tpy)₂ ²⁺ MLCT band. These two low-energy bands derive from mixingof porphyrin Q-state transitions with the Ru(tpy)₂ ²⁺ MLCT transition,enabled by head-to-tail transition dipole alignment of the(porphinato)metal and (terpyridyl)metal chromophoric components.

FIG. 3A shows a representative ultra-fast transient absorption spectrarecorded at several time delays for eDef-Rutpy; and FIG. 3B showsrepresentative ultra-fast transient absorption spectra recorded atseveral time delays for eDef-RuPZn. Experimental conditions included:solvent=acetonitrile; temperature=21° C.; magic angle polarization;eDef-Rutpy: λ_(ex)=480 nm, P_(ex)=1 μJ/Pulse; eDef-RuPZn: λ_(ex)=620 nm,P_(ex)=870 nJ/pulse.

As reflected in FIGS. 3A and 3B, ultrafast transient absorptionexperiments demonstrate excited-state dynamics for eDef-Rutpy andeDef-RuPZn in acetonitrile solvent similar to those of theirelectron-rich counterparts (see Duncan, T. V.; Rubtsov, I. V.; Uyeda, H.T.; Therien, M. J. J. Am. Chem. Soc. 2004, 126, 9474; Duncan, T. V.;Ishizuka, T.; Therien, M. J. J. Am. Chem. Soc. 2007, 129, 9691;Singh-Rachford, T. N.; Nayak, A.; Muro-Small, M. L.; Goeb, S.; Therien,M. J.; Castellano, F. N. J. Am. Chem. Soc. 2010, 132, 14203; and Nayak,A.; Park, J.; De Mey, K.; Hu, X.; Duncan, T. V.; Beratan, D. N.; Clays,K.; Therien, M. J. ACS Cent. Sci. 2016, 2, 954).

Excitation of eDef-Rutpy at 480 nm, as shown in FIG. 3A, generates thebroad featureless transient absorption characteristic of the ³MLCT statewithin the 200 fs time resolution of the instrument. As shown in FIG.12A, the 1 ns ³MLCT state lifetime of eDef-Rutpy is 4 times longer thanthe 250 ps lifetime of Ru(tpy)₂ ²⁺, likely due to ³MC statedestabilization relative to the ³MLCT state, resulting from —CF₃substitution.

Excitation of eDef-RuPZn at 620 nm, as shown in FIG. 3B, generates anintense NIR transient absorption manifold that becomes more intense uponS₁→T₁ intersystem crossing (ISC) to the long-lived T₁ charge-transferstate. For eDef-RuPZn, the 13.5 ps S₁→T₁ ISC time constant and the 93 μsT₁ excited-state lifetime (see FIGS. 13-16) are extended by at least twoorders of magnitude relative to the sub-100 fs ISC time constants andns-timescale T₁ lifetimes characteristic of Ru(tpy)₂ ²⁺ and itsderivatives (see Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E.C.; Thompson, A. M. W. C. Inorg. Chem. 1995, 34, 2759; and Pal, A. K.;Hanan, G. S. Chem. Soc. Rev. 2014, 43, 6184.).

Long excited-state lifetimes of photo-oxidants are crucial for achievinghigh yields of desired photoreactions. For instance, sub-ps timescaleelectron injection from the short-lived ¹MLCT states of Ru(II)polypyridyl complexes into TiO₂ semiconductor interfaces cannottypically proceed with unit quantum yield; hence, a substantial degreeof electron injection occurs from the energetically lower ³MLCT statesover the 10-100 ps time domain. Given the magnitudes of the respectiveeDef-RuPZn S₁- (13.5 ps) and T₁-state (93 ps) lifetimes, it is clearthat this chromophore design offers not only new opportunities toachieve high-yield charge injection at semiconductor interfaces, but thepossibility to engineer energy conversion systems that realizesubstantial electron transfer quenching of the ¹eDef-RuPZn* state,before energy-wasting ¹MLCT→³MLCT ISC can occur.

FIG. 4 illustrates redox potentials from potentiometric data of Ru(tpy)₂²⁺, eDef-Rutpy, RuPZn and eDef-RuPZn. The Left Panel shows ground-stateRu(tpy)₂ ²⁺, eDef-Rutpy, RuPZn and eDef-RuPZn potentiometric data; andthe Right Panel shows corresponding S₁- and T₁-state redox propertiesfor these chromophores (The calculations of the redox properties aredescribed in detail in the section entitled “Calculation of ExcitedState Redox Potential” herein).

FIGS. 13 and 14 show potentiometric data of eDef-Rutpy and eDef-RuPZn,respectively. Potentiometric data acquired for eDef-Rutpy and eDef-RuPZnreveal that perfluoroalkyl substitution raises the E^(0/+) values ofthese chromophore motifs by ˜0.5 V relative to their respectivechromophoric benchmarks.

Note that the measured E_(1/2)(Ru^(2|/3|)) value for eDef-Rutpy (2.05 V)is ˜300 mV higher than the Ru^(2+/3+) potentials realized forelectron-poor Ru(tpy)₂ ²⁺ derivatives that feature extensive —CN/—NO₂substitution (see Fallahpour, R. A.; Neuburger, M.; Zehnder, M. New J.Chem. 1999, 23, 53; Wang, J. H.; Fang, Y. Q.; Hanan, G. S.; Loiseau, F.;Campagna, S. Inorg. Chem. 2005, 44, 5), and ˜200 mV higher than thatreported for Ru(dqxp)₂ ²⁺, a chromophore having the highestE_(1/2)(Ru^(2+/3+)) potential yet established for tridentate Ru(II)complexes (see Pal, A. K.; Hanan, G. S. Chem. Soc. Rev. 2014, 43, 6184).

Similarly, the E_(1/2)(eDef-RuPZn)^(0/+) potential (1.63 V) is more than0.5 V larger than that determined for RuPZn (see also Uyeda, H. T.;Zhao, Y. X.; Wostyn, K.; Asselberghs, I.; Clays, K.; Persoons, A.;Therien, M. J. J. Am. Chem. Soc. 2002, 124, 13806; and Duncan, T. V.;Ishizuka, T.; Therien, M. J. J. Am. Chem. Soc. 2007, 129, 9691). Notethat the eDef-RuPZn E^(0/+) value is remarkably high for a largen-conjugated system. While n-conjugation expansion is a common approachby which panchromatic absorptivity may be realized, it can come at theexpense of a destabilized HOMO level that diminishes E_(1/2) ^(0/+):here broad high-oscillator strength vis domain spectral absorptivityderives from the multi-directional CT nature of low-lying eDef-RuPZnexcited states, preserving a substantial E_(1/2) ^(0/+).

Excited-state redox potentials (E^(−/)* and E*^(/+)) of eDef-Rutpy andeDef-RuPZn determine thermodynamic driving forces (ΔG) forphoto-reduction and photo-oxidation reactions. The S₁-state reductionpotential (¹E^(−/)*=1.59 V) of eDef-RuPZn is impressive, even slightlyhigher than that of Ru(CN-tpy)₂ ²⁺, which has the highest excited-statereduction potential among established tridentate Ru(II) complexes (seeWang, J. H.; Fang, Y. Q.; Hanan, G. S.; Loiseau, F.; Campagna, S. Inorg.Chem. 2005, 44, 5), but much poorer absorptivity than eDef-RuPZn and anexcited state lifetime two orders of magnitude shorter then eDef-RuPZn.

In the context of DSPEC architectures, comparison of the chromophoreE*^(/+) values with the conduction band onsets of semiconductorelectrodes evaluates the feasibility of photoinduced electron injectionto generate (chromophore)^(|) species that may perform desired oxidativechemistry. The S₁ state E*^(/+) value of eDef-RuPZn is −0.35 V,indicating an exergonic ΔG for electron injection into SnO₂, a popularsemiconductor electrode material with a low conduction band onset of 0 V(vs. NHE) at neutral pH (see Knauf, R. R.; Brennaman, M. K.; Alibabaei,L.; Norris, M. R.; Dempsey, J. L. J. Phys. Chem. C 2013, 117, 25259).The 13.5 ps S₁-state lifetime of eDef-RuPZn, two orders of magnitudelonger than those of conventional Ru(II) terpyridyl derivatives,suggests opportunities to realize high quantum yield S₁ state electroninjection; it is also important to underscore that in circumstanceswhere eDef-RuPZn ISC dynamics prevail over electron injection from theS₁ state, electron injection remains thermodynamically viable from thelong-lived (93 μs) T₁ state. The potential of the (eDef-RuPZn)^(⋅+) hole(1.63 V vs. NHE) is comparable with the reduction potential of thestrong chemical oxidant Ce(NH₄)₂(NO₃)₆ see Blakemore, J. D.; Schley, N.D.; Balcells, D.; Hull, J. F.; Olack, G. W.; Incarvito, C. D.;Eisenstein, O.; Brudvig, G. W.; Crabtree, R. H. J. Am. Chem. Soc. 2010,132, 16017), suggesting the breadth of chemistry that could be driven byDSPECs incorporating this high-potential panchromatic chromophore.

In contrast to the described photo-oxidents, established photo-oxidantssuch as porphyrin derivatives, perylene diimides, and metal complexesexhibit limited visible spectral coverage. Enhancement oflong-wavelength oscillator strength by extending n-conjugation typicallycomes at the expense of a lower E^(0/+) value (HOMO destabilization),thus diminishing the ΔG for oxidative chemistry. However, the compoundsdescribed herein can express a high potential (E^(0/+) value) whileproviding a long-wavelength oscillator strength. Indeed, the specificexample of a high-potential (terpyridyl)metal-based chromophore havingpanchromatic UV-vis spectral domain absorptivity, with an integratedvisible oscillator strength eight fold greater than those of typicalRu(II) terpyridyl complexes shows promise for photo-oxidation.eDef-RuPZn is a panchromatic chromophore with a E_(1/2)° ⁴ potentialcomparable to that of Ce(NH₄)₂(NO₃)₆, [E_(1/2)(Ce^(3+/4+))=1.61 V vs.NHE], which affords eDef-RuPZn with an uncommonly large excited-statereduction potential (¹E^(/)*=1.59 V; ³E^(/)*=1.26 V).

As can be seen, eDef-Rutpy, a chromophore having the highest E^(0/+)value of any known Ru(II) bis(tridentate) complex, along with acorresponding ethyne-bridged eDef-Rutpy(porphinato)Zn(II) (eDef-RuPZn)supermolecule is endowed with intense panchromatic absorptivity, a largemagnitude excited-state reduction potential (e.g., (¹E^(−/)*=1.59 V;³E^(−/)*=1.26 V), and long-lived (e.g., S₁- (13.5 ps) and T₁-state (93μs) lifetimes), highly oxidizing singlet and triplet charge-transfer(CT) excited states.

A greater understanding of the present invention and of its manyadvantages may be had from the following example, given by way ofillustration. The following examples are illustrative of some of thesystems, methods, applications, embodiments and variants of the presentinvention. They are, of course, not to be considered in any waylimitative of the invention. Numerous changes and modifications can bemade with respect to the invention.

In general, an amount, size, formulation, parameter or other quantity orcharacteristic is “about” or “approximate”, reflecting tolerances,conversion factors, rounding off, measurement error and the like, andother factors known to those of skill in the art, whether or notexpressly stated to be “about” or “approximate”.

Unless stated otherwise, all percentages, parts, ratios, etc., are byweight.

Further, when an amount, concentration, or other value or parameter isgiven as either a range, preferred range or a list of upper preferablevalues and lower preferable values, this is to be understood asspecifically disclosing all ranges formed from any pair of any upperrange limit or preferred value and any lower range limit or preferredvalue, regardless of whether ranges are separately disclosed. Where arange of numerical values is recited herein, unless otherwise stated,the range is intended to include the endpoints thereof, and all integersand fractions within the range. It is not intended that the scope of theinvention be limited to the specific values recited when defining arange. When a component is indicated as present in a range starting from0, such component is an optional component (i.e., it may or may not hepresent). When present, an optional component may be present at a levelof at least 0.1 weight % of the composition, unless present at s.pecilied lower amounts.

Chemical Synthesis of eDef-Rutpy and eDef-RuPZn

FIG. 5 illustrates a synthetic route to eDef-Rutpy and eDef-RuPZnaccording to an example method. All charged compounds featurePF₆-counter-anions.

Referring to FIG. 5, intermediates (1), (2), (3), (4), (5), (6), and (7)are used to synthesize eDef-Rutpy and eDef-RuPZn. Trials of using only(5) and RuCl₃ hydrate as starting materials for synthesizing eDef-Rutpydid not succeed. Instead, eDef-Rutpy was obtained from the reaction inwhich (5), (7) and RuCl₃ hydrate were used (heteroleptic coordinationproduct was also obtained), as shown in FIG. 5.

Ethyl-4-trifluoromethylpicolinate (1). N-BuLi (3.6 ml, 9 mmol) was addeddropwise to a solution of 2-bromo-4-trifluoromethylpyridine (1.0 ml, 8.1mmol) in THF (50 ml) at −100° C. After 30 min at the same temperature,ethyl formate (6.5 ml, 81 mmol) was added to the mixture and thesolution was stirred at −78° C. for another 3 h. EtOH (12 ml), K₂CO₃(3.3 g, 24 mmol) and I₂ (6 g, 24 mmol) were then added; the reactionmixture was allowed to warm up and react for 15 h at RT (roomtemperature). After the reaction was complete, saturated Na₂SO₃ aqueoussolution was added to quench excess I₂, and the crude product wasextracted with DCM. The organic layer was dried with Na₂SO₄ salt andsolvent was removed. The remaining crude product was purified by neutralalumina column chromatography (DCM:hexanes=3:1) to give a colorless oil(230 mg, 31%).

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.95 (d, 1H, J=4 Hz), 8.35 (s, 1H), 7.70(d, 1H, J=4 Hz), 4.51 (q, 2H, J=8 Hz), 1.46 (t, 3H, J=8 Hz).

C₉H₈F₃NO₂: m/z=219.05, MS: m/z=220.12 [M+H]⁺.

1,5-Bis(4-(trifluoromethyl)pyridin-2-yl)pentane-1,3,5-trione (2). NaH(60% dispersion in mineral oil, 668 mg, 16.7 mmol) was suspended in dryDME (10 ml). A solution of acetone (0.245 ml, 3.33 mmol) and (1) (2.18g, 10 mmol) in DME (20 ml) were added. The reaction was then stirred at90° C. for 6 h and a brownish suspension was obtained. After carefulremoval of the solvent, H₂O was added slowly and the mixture wasneutralized with HCl. A dark yellow solid was obtained by filtration andwas directly used in the next step (1.3 g, 33%).

4,4″-Bis(trifluoromethyl)-[2,2′,6′,2″-terpyridin]-4′(1′H)-one (3). Asolution of (2) (890 mg, 3 mmol) and NH₄OAc (4 g, excess) in EtOH (50ml) was refluxed for 6 h. After removing the solvent, DCM and H₂O wereadded to extract the crude product. The organic layer was washed withsaturated NaHCO₃ (aq) solution. The crude product was purified by SiO₂column chromatography (DCM:methanol=92:8) to give a yellow solid (200mg, 72%) that was used for the next step without further purification.

4′Bromo-4,4″-bis(trifluoromethyl)-2,2′,6′,2″-terpyridine (4). Thebrominated electron-deficient ligand (4) was synthesized by modifying anestablished synthetic procedure of terpyridine, such as described byUshijima, S.; Moriyama, K.; Togo, H. Tetrahedron 2012, 68, 4701 andConstable, E. C.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1990, 1405.In particular, a mixture of (3) (200 mg, 0.52 mmol), PBr₅ (336 mg, 0.78mmol) and POBr₃ (1.6 g, excess) was heated at 100° C. for 16 h,following which, H₂O and saturated NaHCO₃ (aq) solution were slowlyadded to neutralize the reaction. The crude product was then extractedwith DCM. Purification by SiO₂ column chromatography using DCM as theeluent gave a white solid as the product (150 mg, 65%).

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.88 (d, 2H, J=4 Hz), 8.77 (s, 2H), 8.73(s, 2H), 7.59 (d, 2H, J=4 Hz).

C₁₇H₈BrF₆N₃: m/z=448.98, MS: m/z=450.04 [M+H]^(|).

4,4′,4″-Tris(trifluoromethyl)-2,2′,6′,2″-terpyridine (5). N-BuLi (3.6ml, 9 mmol) was added dropwise to a solution of2-bromo-4-trifluoromethylpyridine (1.0 ml, 8.1 mmol) in THF (50 ml) at−100° C. After 30 min at the same temperature, ZnCl₂ (1.1 g, 8.1 mmol)in THF (5 ml) was added dropwise. The reaction mixture was then left towarm up to room temperature. After 2 h, the reaction mixture was addedto a THF solution (5 ml) of Pd(PPh₃)₄ (936 mg, 0.81 mmol) and2,6-dichloro-4-trifluoromethylpyridine (0.46 ml, 3.24 mmol), and heatedto 70° C. After 16 h, the reaction was cooled to room temperature, and50 ml saturated EDTA solution (adjusted to PH=10) was added. The crudeproduct was extracted with dichloromethane. The organic layer was driedover Na₂SO₄ and the solvent was removed. The remaining crude waspurified by silica column chromatography (DCM:hexanes=1:1) to give awhite solid (120 mg, 8.5%).

¹H NMR (400 MHz, CDCl₃, ppm): δ 8.93 (d, 2H, J=4 Hz), 8.81 (s, 4H), 7.64(d, 2H, J=4 Hz).

C₁₈H₁₈H₈F₉N₃: m/z=437.06, MS: m/z=438.21 [M+H]⁺.

eDef-TpyRuCl₃ ³⁺ (6). A suspension of (5) (100 mg, 0.23 mmol) and RuCl₃hydrate (51.4 mg, 0.23 mmol) in 20 ml ethanol was heated at reflux for 3h. The solvent was then evaporated to a volume of 5 ml; the mixture wasfiltered and the resulting precipitate was washed with diethyl ether,dried, and used directly for the next step.

eDef-RutpyBr. A suspension of (6) (50 mg, 0.077 mmol) and (4) (36 mg,0.080 mmol) in 5 ml ethylene glycol was heated at 150° C. for 80 min(heating for too long will cause debromination). Then 10 ml saturatedKPF₆ solution was added. The precipitate was collected by vacuumfiltration and purified by silica column chromatography(MeCN:H₂O:saturated KNO₃(aq)=95:4:1). The first red bands wereconcentrated to 5 ml and saturated KPF₆ solution was added to give a redprecipitate (30 mg, 30%).

¹H NMR (400 MHz, d³-MeCN, ppm): δ 9.26 (s, 2H), 9.23 (s, 2H), 8.94 (s,2H), 8.79 (s, 2H), 7.68 (d, 2H, J=4 Hz), 7.58 (d, 2H, J=4 Hz), 7.53 (d,2H, J=4 Hz), 7.46 (d, 2H, J=4 Hz).

C₃₅H₁₆BrF₁₅N₆Ru: m/z=985.94, MALDI-TOF: m/z=986.35 [M]⁺, 1131.55[M+PF₆]⁺.

Synthesis of P₃Tpy ligand (7) was adapted from established syntheticprocedures (see Duncan, T. V.; Ishizuka, T.; Therien, M. J. J. Am. Chem.Soc. 2007, 129, 9691). Note that in contrast to perfluoroalkylatedtris(bipyridyl)Ru(II) complexes (see Furue, M.; Maruyama, K.; Oguni, T.;Naiki, M.; Kamachi, M. Inorg. Chem. 1992, 31, 3792), eDef-Rutpy speciesenable panchromatic chromophore design strategies that can takeadvantage of the RuPZn design motif that optimally mixes porphyrinligand π-π* and (polypyridyl)metal charge transfer states (see RuPZnsynthesis as described in yeda, H. T.; Zhao, Y. X.; Wostyn, K.;Asselberghs, I.; Clays, K.; Persoons, A.; Therien, M. J. J. Am. Chem.Soc. 2002, 124, 13806; Duncan, T. V.; Rubtsov, I. V.; Uyeda, H. T.;Therien, M. J. J. Am. Chem. Soc. 2004, 126, 9474; and Duncan, T. V.;Ishizuka, T.; Therien, M. J. J. Am. Chem. Soc. 2007, 129, 9691).

eDef-Rutpy. A suspension of (5) (20 mg, 0.046 mmol) and RuCl₃ hydrate(10.3 mg, 0.046 mmol) in 5 ml ethylene glycol was heated at reflux for 3h. Then (7) (22 mg, 0.050 mmol) and 5 ml methanol were added and themixture was refluxed for another 3 h. After that, 10 ml saturated KPF₆solution was added. The precipitate was collected by vacuum filtrationand purified by silica column chromatography (MeCN:H₂O:saturatedKNO₃(aq)=95:4:1). The first red bands were concentrated to 5 ml andsaturated KPF₆ solution was added to provide a red precipitate (9 mg,20%).

¹H NMR (400 MHz, d³-MeCN, ppm): δ 9.28 (s, 4H), 8.95 (s, 4H), 7.63 (d,4H, J=4 Hz), 7.52 (d, 4H, J=4 Hz).

C₃₆H₁₆F₁₈N₆Ru: m/z=976.02, MALDI-TOF: m/z=976.86 [M]⁺, 1121.43 [M+PF₆]⁺.

eDef-RuPZn. Perfluoroalkyl porphyrin (Rf₃PZnETIPS) (22.8 mg, 0.0215mmol) in 50 ml THF was cooled down in an ice water bath.Tetra-n-butylammonium fluoride (25 ul, 0.025 mmol) was added to removethe triisopropylsilyl protecting-group of Rf₃PZnETIPS. After TLC showedcompletion of the reaction, the solvent was removed and Rf₃PZnE waschromatographed on silica (THF:hexanes=95:5). A 100 mL Schlenk flaskequipped with a stirbar was charged with Rf₃PZnE (from 22.8 mgRf₃PZnETIPS), eDef-RutpyBr (25 mg, 0.0196 mmol), Pd₂(dba)₃ (3.6 mg,0.004 mmol) and AsPh₃ (6 mg, 0.0196 mmol) under Ar, following which 20ml THF, 20 ml acetonitrile and 4 ml diisopropylamine were mixed togetherand added after being degassed by 3 freeze-pump-thaw cycles. The mixturewas heated at 60° C. overnight. When the reaction was complete, most ofthe solvent was removed. A small amount of acetonitrile was added todissolve the mixture. Saturated KPF₆ aqueous solution was added toprecipitate the product. The crude product was filtered and dried. Thecompound was then purified by silica gel chromatography(MeCN:H₂O:saturated KNO₃ (aq)=96:3:1). eDef-RuPZn was collected, and theeluent evaporated to a volume of 30 ml; saturated ammoniumhexafluorophosphate was added to precipitate the product, which was thenfiltered and dried to give a brownish solid (21 mg, %, based oneDef-RutpyBr).

¹H NMR (400 MHz, d³-MeCN, ppm): δ 10.32 (d, 2H, J=6 Hz), 9.79 (s, 2H),9.73 (s, 2H), 9.67 (m, 4H), 9.32 (s, 2H), 9.13 (s, 2H), 9.00 (s, 2H),7.85 (d, 2H, J=6 Hz), 7.67 (d, 2H, J=6 Hz), 7.61 (d, 2H, J=6 Hz), 7.57(d, 2H, J=6 Hz).

C₆₆H₂₄F₃₆N₁₀RuZn: m/z=1805.99, MALDI-TOF: m/z=1806.64 [M]⁺, 2096.33[M+2PF₆]⁺.

Synthetic Materials: All manipulations were performed under argonprepurified by passing through an O₂ scrubbing tower packed withSchweizerhall R3-11 catalyst and a drying tower packed with Linde 3 Åmolecular sieves. Air-sensitive solids were weighed in a Braun 150-Mglove box. Standard Schlenk techniques were employed to manipulateair-sensitive solutions. Tetrahydrofuran (THF) was purchased fromSigma-Aldrich (Inhibitor free, HPLC grade) and distilled over sodium andbenzophenone before use. Diisopropylamine was purchased fromSigma-Aldrich. All other solvents utilized in synthesis described inthis work were purchased from Fisher Scientific (HPLC grade).Acetonitrile were dried over calcium hydride and distilled. All otherreagents were used as received (Aldrich or Fisher).

Instrumentation

A 400 MHz Brüker spectrometer was used to obtain NMR spectra for allsynthesized compounds. Chemical shifts for ¹H NMR spectra are reportedrelative to residual protium in deuterium solvent (6 (residual)=7.26 ppmin CDCl₃, δ (residual)=1.94 ppm in d³-MeCN). All J values are reportedin Hertz. Reported MALDI-TOF data were acquired with an AppliedBiosystems DE-Pro Maldi-MS at the Department of Chemistry in DukeUniversity. Samples were prepared as micromolar solutions in acetone,using HABA (2-(4-Hydroxyphenylazo)benzoic acid) as the matrix. ReportedMS data were acquired with an Agilent LC/MSD Trap at the Department ofChemistry in Duke University. Electronic absorption spectra wereacquired on a Shimadzu Pharmaspec UV-1700 spectrometer.

FIG. 6 shows Proton NMR spectrum of eDef-Rutpy in CD₃CN; and FIG. 7shows Proton NMR spectrum of eDef-RuPZn in CD₃CN.

FIG. 8 shows Electronic absorption spectrum of RuPZn in acetonitrilesolvent.

FIG. 9 shows Electronic absorption spectra of eDef-RuPZn (in MeCN),eDef-Rutpy (in MeCN) and[5-ethynyl-10,15,20-tris(heptafluoropropyl)porphinato]zinc(II) (in THF)building blocks; and room-temperature emission spectra (fluorescence at700 nm and phosphorescence at 810 nm, excitation wavelength=628 nm) ofeDef-RuPZn in acetonitrile solvent; the sample was degassed via threefreeze-pump-thaw cycles prior to data collection.

FIG. 10A shows a 77K Emission spectrum (excitation wavelength=510 nm) ofeDef-Rutpy in butyronitrile, and the absorption spectrum of eDef-Rutpyat RT (room temperature) in acetonitrile; FIG. 10B shows a Gaussianfitting of the 77K emission data of FIG. 10A, with labeled energy (2.09eV) at which the emission intensity is 10% that of the highest emissionintensity.

FIG. 11 shows a 77K emission spectrum (fluorescence at 600750 nm andphosphorescence at 750˜850 nm, excitation wavelength=590 nm) ofeDef-RuPZn in butyronitrile, and the absorption spectrum of eDef-RuPZnin acetonitrile. As can be seen from FIG. 11, the intersection point ofthe absorption and emission spectra is at 626 nm.

FIG. 12A shows plots of a room-temperature (RT) emission spectrum(excitation wavelength=628 nm) of eDef-RuPZn in deaerated acetonitrilesolvent, 77K emission spectrum (excitation wavelength=628 nm) ofeDef-RuPZn in butyronitrile, along with the absorption spectrum ofeDef-RuPZn in acetonitrile. FIG. 12B shows Gaussian fitting of the RTemission data of FIG. 12A, with labeled energy (1.65 eV) at which theemission intensity is 10% that of the highest emission intensity. FIG.12C shows Gaussian fitting of the 77K emission data of FIG. 12A onenergy scale, with labeled energy (1.61 eV) at which the emissionintensity is 10% that of the highest emission intensity.

Cyclic voltammetry and differential pulse voltammetry experiments wereperformed on a BASi EC Epsilon working station, using an Ag/AgCl (3MNaCl) reference electrode, a Pt wire counter electrode, and a glassycarbon working electrode. The ferrocene/ferrocenium redox couple (0.43 Vvs. SCE, 0.67 V vs. NHE) was used as an internal standard.

FIG. 13 shows potentiometric data of eDef-Rutpy (vs. SCE) in 0.1 MTBAPF₆/acetonitrile electrolyte/solvent system. The plots show thecyclic voltammetric response and the differential pulse voltammetry(DPV) measurement.

FIG. 14 shows potentiometric data of eDef-RuPZn (vs. SCE) in 0.1 MTBAPF₆/acetonitrile electrolyte/solvent system. The plots show thecyclic voltammetric response and the DPV measurement. Reported redoxpotential values correspond to those obtained from the DPV experiment.

Femtosecond-to-Nanosecond Timescale Pump-Probe Transient AbsorptionSpectroscopy

FIG. 15 shows representative time traces (black) from femtosecondpump-probe transient absorption of eDef-Rutpy in acetonitrile solventfor 461 nm, 499 nm, 520 nm, and 738 nm wavelengths. A global fit to thedynamics indicates a mono-exponential lifetime of ˜1 ns. Experimentalconditions for these plots: Magic angle polarization, T=21° C., pumppower=1 μJ/pulse, Excitation wavelength=480 nm.

FIG. 16 shows representative time traces (black circles) fromfemtosecond pump-probe transient absorption of eDef-RuPZn inacetonitrile solvent for 509 nm, 533 nm, 607 nm, 668 nm, 732 nm, 824 nm,901 nm, and 1010 nm wavelengths. FIG. 17 shows plots of decay-associateddifference spectra (DADS) of eDef-RuPZn derived from a global fit ofpump-probe transient absorption data from FIG. 13 in acetonitrilesolvent. In FIG. 16, each time trace is shown with its correspondingglobal fit to the dynamics, and time constants are as shown in FIG. 17.In FIG. 16, the signal at long-time-delay derives from T₁→T_(N)transient absorption from the long-lived triplet state. Experimentalconditions for these plots: Magic angle polarization, T=21° C., pumppower=870 nJ/pulse, Excitation wavelength=620 nm.

Ultrafast transient absorption spectra were obtained using standardpump-probe methods, such as described by Rubtsov, I. V.; Susumu, K.;Rubtsov, G. I.; Therien, M. J. J. Am. Chem. Soc. 2003, 125, 2687; Park,J.; Deria, P.; Therien, M. J. J. Am. Chem. Soc. 2011, 133, 17156; andPark, J.; Deria, P.; Olivier, J. H.; Therien, M. J. Nano Lett. 2014, 14,504. Optical pulses (≥120 fs) centered at 775 nm, were generated using aTi:Sapphire laser (Clark-MXR, CPA-2001, Dexter, Mich., USA), whichconsisted of a regenerative amplifier seeded by a mode-locked fiberoscillator. The output of the regenerative amplifier was split to feedan optical parametric amplifier (Light Conversion Ltd., TOPAS-C,Vilnius, Lithuania), which generates excitation pulses tunable inwavelength from the UV through the NIR region. The pump beam was choppedat half the laser repetition rate (˜500 Hz). A fraction (<5%) of theoutput from the regenerative amplifier was passed through an opticaldelay line, and focused onto a 2 mm c-cut sapphire plate to generate awhite light continuum, which was used as the probe beam. Thepolarization and attenuation of the pump and probe beams were controlledby half-wave plate and Rochon prism polarizer pairs. The polarizationwas set to the magic angle (54.7°) for these experiments.

The pump beam was focused into the sample cell with an f=20 cm lens,while the probe beam was focused with a parabolic mirror. The pump spotsize diameter was ˜0.3 mm. The beam diameter was determined using therazor-blade method. The excitation pump power was measured using a powermeter (Coherent, LabMax Top with PS19 head). After passing through thesample, the probe light was adjusted using a neutral density filter toavoid saturating the detector, and focused onto the entrance slit of acomputer-controlled image spectrometer (Acton Research Corporation,SpectraPro-150, Trenton, N.J., USA). A CCD array detector (1024×128elements, Roper Scientific, Trenton, N.J., USA), interfaced to thespectrometer, recorded the spectrum of the probe light from the UV (˜370nm) to the NIR (˜1100 nm), providing spectral resolution better than 0.5nm. Pairs of consecutive spectra were measured with I_(on)(λ) andI_(off)(λ) to determine the difference spectrum,ΔA=log(I_(off)(λ)/(I_(on)(λ)). All these experiments utilized acustom-built 2 mm-path-length fused-silica sample cell; all transientoptical studies were carried out at 21±1° C. in HPLC grade acetonitrilesolvent received from Sigma-Aldrich. All transient spectra reportedrepresent averages obtained over 3-5 scans, with each scan consisting of˜300 time delays spaced on a log scale, with each time delay an averageof 3000 frames.

In these experiments, the optical delay line utilizes acomputer-controlled delay stage. Delay times up to 4 ns were achievedusing a Compumotor-6000 (Parker). The baseline noise level in thesetransient absorption experiments corresponded to ˜0.2 mOD per second ofsignal accumulation. The time resolution is probe-wavelength dependent;in these experiments, the FWHM of the instrument response function (IRF)varied between 140-200 fs (e.g., at 680 nm, the IRF was 150±6 fs).Following all pump-probe transient absorption experiments, electronicabsorption spectra verified that the samples were robust. All reportedpump-probe experiments were repeated at least three times withseparately prepared samples.

Nanosecond-to-Microsecond Timescale Pump-Probe Transient AbsorptionSpectroscopy

FIG. 18 shows a plot of nanosecond pump-probe transient absorptionspectra of eDef-RuPZn in acetonitrile solvent following excitation at520 nm. The inset shows kinetics at a representative wavelength overlaidwith single-exponential fit (t =92.5 ps).

Nanosecond transient absorption spectra were acquired utilizing anEdinburgh Instruments LP920 Laser Flash Photolysis Spectrometer andEdinburgh L900 Software. Pump pulses were generated from a Q-switchedNd:YAG laser (Quantel, Brilliant) and a dual-crystal OPO (OPOTEK,Vibrant LDII). The temporal width of the pump pulses was ˜5 ns; theenergy of the pulses exiting the OPO was controlled using neutraldensity filters. A Xe flash-lamp was used as a white light probe source,and a CCD array detector enabled acquisition of transient data over the400-800 nm wavelength domain. A PMT detector coupled to an oscilloscopeallowed for high-resolution data acquisition in “kinetic mode.” Both theLP920 and Opotek OPO are computer interfaced and controlled by the L900software. Transient spectra reported derive from data acquired over˜20-50 scans. Samples were prepared in 1 cm quartz cells and de-aeratedby 3 freeze-pump-thaw degas cycles prior to excitation. Excited-statelifetimes were calculated via mono-exponential fitting using Origin 9.1software.

Time-Resolved Emission Spectroscopy

FIG. 19 shows a time-resolved emission of RuPZn in acetonitrile solventwith its fit to a mono-exponential function convoluted with theexperimentally determined instrument response function (IRF).Magic-angle polarization time-resolved emission data were recorded usinga Hamamatsu C4780 picosecond fluorescence lifetime measurement system,which utilizes a Hamamatsu Streakscope C4334 photoncounting detector, aHamamatsu C4792-01 synchronous delay generator, and a Stanford ResearchSystems DG535 electronic delay generator. RuPZn was excited by aHamamatsu PLP-10 laser diode (405 nm), and the polarization of emissionwas set to the magic angle (54.7°) for these experiments. HamamatsuHPD-TA software was used to acquire emission data in the single-photoncounting mode, and its fitting module was used to fit the emissionlifetime by deconvolution with the experimentally determined instrumentresponse function (irf). The irf was measured using a scattering sample(cream dissolved in water or silica in water). Sample concentrationswere adjusted to give an optical density of 0.1 at the excitationwavelength. The time constant from this fit is 18±1 ps, which isidentical to the rise time of the transient absorption signal in thenear-IR measured via pump-probe spectroscopy. Because of the completelyanalogous spectra and dynamics of ED-RuPZn, we assign the 13.5 ps risetime of the transient absorption signal in the near-IR to S₁→T₁intersystem crossing of this electron-deficient supermolecule.Experimental conditions: excitation wavelength=650 nm, magic anglepolarization, T=20° C., emission intensity was integrated over the670-740 nm spectral window.

Calculation of Excited State Redox Potentials

Redox potentials of eDef-Rutpy and eDef-RuPZn S₁ and T₁ states werecalculated from respective E_(0,0) energies and ground state redoxpotentials, such as described by Turro, N. J. Principles of ModernMolecular Photochemistry; University Science Books: Sausolito, Calif.,2009.

The experimental conditions involved: 0.1 M TBAPF₆/acetonitrileelectrolyte/solvent system; ambient temperature; potential vs. NHE; SnO₂conduction band (cyan shadow, onset=0 V) at neutral pH.

eDef-Rutpy is non-emissive at room temperature, but is emissive at 77K.Similar to other Ru(II) polypyridyl complexes, the forbidden S₀→³MLCTtransition of eDef-Rutpy is weak and observed as a low-energy tail inthe electronic absorption spectrum (see Roundhill, D. M. InPhotochemistry and Photophysics of Metal Complexes; Springer US: Boston,Mass., 1994). Due to intensity scaling ambiguities, the T₁ state E_(0,0)energy of eDef-Rutpy is not acquired from the intersection point of theS₀→³MLCT absorption and ³MLCT→S₀ emission, but rather is estimated fromthe ³MLCT emission energy corresponding to 10% intensity of that of thehighest energy emission maximum (the “10% rule”), assuming a Gaussianemission shape (see Dossing, A.; Ryu, C. K.; Kudo, S.; Ford, P. C. J.Am. Chem. Soc. 1993, 115, 5132; and McClure, L. J.; Ford, P. C. J. Phys.Chem. 1992, 96, 6640). Thus the T₁ state E_(0,0) energy of eDef-Rutpy isestimated as 2.09 eV (see FIG. 10B).

³eDef-Rutpy^(−/)*=eDef-Rutpy^(−/0) +E _(0,0)=0.48+2.09=1.61 V

³eDef-Rutpy*^(/|)=eDef-Rutpy^(0/|) −E _(0,0)=2.05−2.09=−0.04 V

The band centered at 700 nm of the emission spectrum of eDef-RuPZn isunaffected by aeration, indicative of S₁→S₀ fluorescence. The intensityof the band peaked at 810 nm is reduced when the sample is aerated,relative to a corresponding deaerated sample; as such, this emissionband corresponds to T₁→S₀ phosphorescence.

The S₁ state E_(0,0) energy of eDef-RuPZn is determined by theintersection of the lowest energy absorption and fluorescence bands:E_(0,0)(S₁)=626 nm=1.98 eV (see FIG. 11).

¹eDef-RuPZn^(−/)*=eDef-RuPZn^(−/0) +E _(0,0)(S ₁)=0.39+1.98=1.59 V

¹eDef-RuPZn*^(/+)=eDef-RuPZn^(0/+) −E _(0,0)(S ₁)=1.63−1.98=−0.35 V

The T₁ state E_(0,0) energy of eDef-RuPZn is assigned according to the“10% rule” discussed above with the 77K emission spectrum:E_(0,0)(T₁)=1.61 eV (see FIG. 12C). With E_(0,0)=1.61 eV, the³E*^(/+)=0.02 eV and is slightly (0.02 eV) more positive than theconduction band onset of SnO₂. However, the spectral breadth ofeDef-RuPZn phosphorescence at RT (see FIGS. 12A and 12B) suggestsinjection into SnO₂ is possible at RT with ³E*^(/+)=−0.02 eV.

³eDef-RuPZn^(−/)*=eDef-RuPZn^(−/0) +E _(0,0)(T ₁)=−0.39+1.65=1.26 V

³eDef-RuPZn*^(/+)=eDef-RuPZn^(0/+) −E _(0,0)(T ₁)=1.63−1.65=−0.02 V

As described by the example, a highly electron-deficient Ru(II) complex(eDef-Rutpy) is synthesized and shown bearing an E_(1/2) ^(0/+)potential more than 300 mV more positive than that of any establishedRu(II) bis(terpyridyl) derivative. In addition, an ethyne-bridgedeDef-Rutpy-(porphinato)Zn(II) (eDef-RuPZn) supermolecule is synthesizedthat affords both panchromatic UV-vis spectral domain absorptivity and ahigh E_(1/2) ^(0/+) potential, comparable to that of Ce(NH₄)₂(NO₃)₆[E_(1/2)(Ce^(3+/4+))=1.61 V vs. NHE], a strong and versatileground-state oxidant commonly used in organic functional grouptransformations. As further shown, eDef-RuPZn exhibits eight-foldgreater absorptive oscillator strength over the 380-700 nm rangerelative to conventional Ru(II) polypyridyl complexes, and impressiveexcited-state reduction potentials (¹E^(−/)*=1.59 V; ³E^(−/)*=1.26 V).eDef-RuPZn manifests electronically excited singlet and tripletcharge-transfer state lifetimes more than two orders of magnitude longerthan those typical of conventional Ru(II) bis(terpyridyl) chromophores,which is beneficial for light-driven oxidation reactions for energyconversion and photocatalysis.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. In addition, anyelements or limitations of any invention or embodiment thereof disclosedherein can be combined with any and/or all other elements or limitations(individually or in any combination) or any other invention orembodiment thereof disclosed herein, and all such combinations arecontemplated with the scope of the invention without limitation thereto.

Any patents or publications mentioned in this specification areindicative of the levels of those skilled in the art to which theinvention pertains. These patents and publications are hereinincorporated by reference to the same extent as if each individualpublication was specifically and individually indicated to beincorporated by reference.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication. One skilled in the art will readily appreciate that thepresent invention is well adapted to carry out the objects and obtainthe ends and advantages mentioned, as well as those inherent therein.The present examples along with the methods described herein arepresently representative of preferred embodiments, are exemplary, andare not intended as limitations on the scope of the invention. Changestherein and other uses will occur to those skilled in the art which areas defined by the scope of the claims.

What is claimed is:
 1. A compound of a formula comprising: A-L-Bwherein: A is a conjugated macrocycle bearing electron withdrawingsubstituents or is electron-accepting relative to hydrogen; B is a metalcomplex bearing electron withdrawing substituents or iselectron-accepting relative to hydrogen; and L is ethynyl, vinyl,thiophenyl, diethynylaryl, divinylaryl, diethynyl(unsaturatedheterocycloalkenyl), divinyl(unsaturated heterocycloalkenyl),diethynyl(unsaturated heterocycloalkynyl), or divynyl(unsaturatedheterocycloalkynyl).
 2. The compound of claim 1, wherein the macrocycleof the conjugated macrocycle is porphyrin, porphycene, rubyrin, rosarin,hexaphyrin, sapphyrin, chlorophyl, chlorin, phthalocyanine,porphyrazine, bacteriochlorophyl, pheophytin, or texaphyrin.
 3. Thecompound of claim 1, wherein the conjugated macrocycle is a porphyrincomplexed to metal atom M₁.
 4. The compound of claim 3, wherein M₁ isZn, Mg, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Cd, Ge, Sn, Hf, Ta,W, Re, Os, Ir, Pt, Au, or Pb.
 5. The compound of claim 1, wherein theconjugated macrocycle bears an electron withdrawing substituent selectedfrom the group consisting of fluoroaryl, fluoroalkyl, fluoro, halo,cyano, and nitro.
 6. The compound of claim 5, wherein the substituent isperfluoroalkyl or perfluoroaryl.
 7. The compound of claim 1, wherein themetal complex is a (polypyridyl)metal species.
 8. The compound of claim7, wherein a polypyridyl ligand of the (polypyridyl)metal species isterpyridyl or bipyridyl.
 9. The compound of claim 1, wherein the metalcomplex is a (poly-heterocyclic)metal species.
 10. The compound of claim1 wherein the metal complex is neutral.
 11. The compound of claim 1,wherein the metal complex is charged.
 12. The compound of claim 1,wherein the metal complex comprises a transition metal.
 13. The compoundof claim 1, wherein the metal complex comprises a Group 8 transitionmetal.
 14. The compound of claim 1, wherein the metal complex comprisesFe, Ru, Os, Re, Ir, Rh, or Pt.
 15. The compound of claim 1, wherein themetal complex bears an electron withdrawing substituent selected fromthe group consisting of fluoroaryl, fluoroalkyl, fluoro, halo, cyano,and nitro.
 16. The compound of claim 1, wherein L is ethynyl.
 17. Thecompound of claim 1, wherein the formula is A-L-B.
 18. The compound ofclaim 1, wherein the formula is A-L-B-L-A.
 19. The compound of claim 1,wherein the formula is B-L-A-L-B.
 20. The compound of claim 1, wherein Ais eDef-Rutpy-(porphinato)Zn(II), B is eDef-RuPZn, and L is ethyne.